If you’re on camera or on stage seated or seated in a meeting where you are exposed, stay still. Fight off the urge to wiggle/swing your leg, tap your toe, pick your nose, drum your fingers, play with the chair, fiddle with your notes, or anything else that draws attention away from your message. Your posture when seated should be based on the same assumption as when you are standing — the appearance of confidence and relaxed, not distracting to your audience, and functional. In addition, it’s better to lean forward towards your audience rather than away, especially if the leaning back includes slumping of any form. Posture rarely is the key to good communication, but it can quickly downgrade your message when it isn’t done correctly. And it’s just a habit. Make it a good one.
Exercise good posture, whether standing or seated.